JP2000292734A - Scanning optical device - Google Patents

Abstract

PROBLEM TO BE SOLVED: To prevent noise such as an air whistle when a rotary polygon mirror is rotated fast. SOLUTION: For a propagation path L1 for a direct propagated sound, i.e., an air peep which is generated at a corner part 1a of a rotary polygon mirror 1 and directly reaches a lid member 60, a propagation path (L1+2L) for a reflected propagated sound which is reflected by a bottom surface 50a of an optical box 50 and reaches the lid member 60 is constituted so that the length is 1/2λ longer; the two sound waves are made to interfere with each other, thereby reducing the vibration of the lid member 60 and the noise.

Description

DETAILED DESCRIPTION OF THE INVENTION

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a scanning optical device used in an image forming apparatus such as a laser beam printer, an LED printer, and a laser facsimile for forming an image on a transfer sheet by an electrophotographic method.

[0002]

2. Description of the Related Art A scanning optical apparatus used in an electrophotographic image forming apparatus such as a laser beam printer or a laser facsimile machine deflects and scans a light beam such as a laser beam with a rotating polygon mirror rotating at a high speed. The scanning light is imaged on a photoreceptor on a rotating drum to form an electrostatic latent image.
Next, the electrostatic latent image on the photoreceptor is visualized into a toner image by a developing device, transferred to a recording medium such as recording paper, sent to a fixing device, and printed by heating and fixing the toner on the recording medium ( Print) is performed.

In recent years, the speed of the scanning optical device has been increased, and a rotating polygon mirror having a rotating speed exceeding 30,000 rpm has been developed.

FIG. 6 shows a main part of a scanning optical device according to a conventional example, which comprises a rotating shaft 103 supported on an optical box 100 via a bearing 102 such as a ball bearing.
And a yoke 105a and a rotor magnet 10 integrally connected to a washer 104 integrated with the rotating shaft 103.
5 and a stator coil 107 fixed to a motor substrate 106 integral with the bearing housing 102a. The rotating polygon mirror 101 includes a holding spring 108a and a spring holding 10
8b, elastic pressing mechanism 108 including G ring 108c, etc.
Is pressed by the washer 104, and is integrated with the rotating shaft 103 and the rotor magnet 105 via the washer 104.

When the stator coil 107 is excited by a drive current supplied from a drive circuit on the motor board 106, the rotor magnet 105 rotates at a high speed together with the rotary polygon mirror 101, and as described above, the rotary polygon mirror 101
Is deflected and scanned by the light beam applied to the.

When the rotary polygon mirror 101 is rotated at a high speed, a dynamic imbalance occurs due to an imbalance in the mass of the entire rotating body including the rotary polygon mirror 101, the rotor magnet 105, the yoke 105a, the washer 104, the elastic pressing mechanism 108, and the like. Is generated, and due to whirling vibration caused by this,
The image quality of the image forming apparatus may be degraded. Therefore,
Balance grooves 109a and 109b are formed on the upper surface of the rotating polygon mirror 101 and the upper surface of the yoke 105a of the rotor magnet 105.
And a weight 110 or the like is adhered thereto to reduce the imbalance of the mass of the rotating body.

[0007]

However, according to the above-mentioned prior art, the wind noise generated at the outer periphery of the rotating polygonal mirror accompanying the high-speed rotation of the rotating polygonal mirror leaks out of the optical box and generates a large noise. Further, there is an unsolved problem such as deterioration of the image performance of the image forming apparatus as a vibration source that vibrates optical components such as an imaging lens via a lid member or the like of the optical box.

SUMMARY OF THE INVENTION The present invention has been made in view of the above-mentioned unresolved problems of the prior art, and provides a scanning optical apparatus which reduces vibration and noise due to wind noise of a rotating polygon mirror, and has high image quality and low noise. It is intended to provide.

[0009]

In order to achieve the above object, a scanning optical apparatus according to the present invention comprises: a rotating polygon mirror for deflecting and scanning a light beam; a deflection scanning means comprising a motor for rotating and driving the rotating polygon mirror; A housing housing the deflection scanning means, wherein the housing has an opposing wall disposed at a distance L satisfying the following relationship from the outer peripheral portion of the rotary polygon mirror. . L ≒ 15c / N · m where c: speed of sound N: number of rotations of rotating polygonal mirror m: number of reflecting surfaces of rotating polygonal mirror

[0010] The opposed wall surface may be a bottom surface of the housing.

[0011] The opposed wall surface may be a bottom surface of a recess provided in a bottom wall of the housing.

[0012] The opposing wall surface may be provided on a curved portion of a bottom wall of the housing.

The opposing wall surface may be an inner surface of a cover member that covers the rotary polygon mirror, and the distance L may satisfy the following relationship. 0.004 <L <c · π · r / 60m, where c: sound velocity r: radius of a circumcircle of the rotating polygon mirror m: number of reflecting surfaces of the rotating polygon mirror

[0014]

In order to prevent wind noise generated at the outer periphery of the rotating polygonal mirror due to high-speed rotation of the rotating polygonal mirror from vibrating the lid member of the optical box as a housing and generating noise, etc. A so-called direct propagation sound is produced by shifting the sound wave of the wind noise that reaches the lid member by being reflected by the bottom surface and the like and the sound wave of the wind noise that reaches the lid member directly from the outer periphery of the rotary polygon mirror by approximately 1/2 wavelength. And the interference of the reflected sound
It is good to attenuate the sound propagating to the lid member.

As described above, the direct propagation sound and the reflection propagation sound are divided by 1 /
In order to shift by two wavelengths, the distance (L) between the bottom surface of the optical box, which is the opposing wall surface facing the outer peripheral portion of the rotating polygonal mirror on the opposite side of the lid member, and the outer peripheral portion of the rotating polygonal mirror is set forth in claim 1. Set to satisfy the expression.

[0016]

Embodiments of the present invention will be described with reference to the drawings.

FIG. 1 is a schematic cross-sectional view showing a main part of a scanning optical apparatus according to a first embodiment. This is a rotary polygon mirror 1 having a plurality of reflecting surfaces on a polygonal cylindrical side surface as an outer peripheral portion. A rotating shaft 3 rotatably supported by an optical box 50 serving as a housing via a bearing 2, a rotor 5 integrally connected to the rotating shaft 3, and a motor substrate integrated with a motor housing 6 a 6, the stator 7 constitutes a motor for rotating the rotary polygon mirror 1 together with the rotor 5. The rotating polygon mirror 1 is connected to the rotor 5 by a holding plate 8 and is integrated with the rotating shaft 3.
A deflection scanning unit is configured together with the motor.

When the stator 7 is excited by the drive current supplied from the drive circuit on the motor board 6, the rotor 5
Rotates together with the rotating shaft 3 and the rotating polygon mirror 1, and deflects and scans a light beam such as a laser beam applied to the reflection surface of the rotating polygon mirror 1.

The optical box 50 incorporates an image forming lens 52 and the like together with the rotary polygon mirror 1 as described later, and the upper opening of the optical box 50 is closed by a lid member 60.

During the operation of the scanning optical apparatus, wind noise is generated by the rotation of the rotary polygon mirror 1, and noise and vibration due to the wind noise become a problem as the apparatus speeds up. The mechanism by which the noise due to wind noise increases is as follows.

As shown in FIG. 1B, the rotary polygon mirror 1
Has a peripheral speed of 30 m / at the corner 1a where the reflecting surfaces meet.
In the high-speed rotation region of s or more, a turbulent state occurs on the reflection surface behind the corner 1a in the rotation direction, and a so-called Karman vortex S is generated. The impact sound of the generation and disappearance of this vortex increases wind noise. (See JP-A-6-289315).

The frequency ν of the wind noise caused by the Karman vortex S
Is the number of surfaces (the number of reflecting surfaces) of the rotating polygon mirror 1 and the number of rotations is N.
(Rpm), it is represented by the following equation. ν = N · m / 60 (1)

This wind noise causes the lid member 60 to vibrate and becomes a noise that propagates outside the scanning optical device, and also serves as a vibration source that vibrates the entire optical box 50, and
The image quality is degraded due to the vibration of optical components such as the imaging lens 52 (see FIG. 5) built in the camera.

Therefore, the vibration of the lid member 60 due to the wind noise is attenuated as follows. The distance from the corner 1a of the outer peripheral portion, which is the noise generating point (noise source) of the rotary polygon mirror 1, to the lid member 60 is L ₁ , and the corner 50a of the noise source is the bottom surface 50a of the optical box 50 which is the opposing wall surface. Let L be the distance to.

The sound propagation path (2L + L ₁ ) reflected from the corner 1a of the noise source on the bottom surface 50a of the optical box 50 and reaching the lid member 60 is the sound propagation path L ₁ directly propagating to the lid member 60. If the distance L is set to be longer by λλ as the wavelength λ of the propagation sound, the two sound waves propagating to the lid member 60 interfere with each other to attenuate the wind noise,
Trouble caused by wind noise can be reduced. That is,
By delaying the phase of the reflected propagation sound by 波長 wavelength with respect to the directly propagated sound, troubles such as vibration and noise of the lid member 60 can be avoided. The above condition is represented by the following equation. (2 × L + L ₁ ) −L ₁ = (1/2) λ (2) From equation (2), L = (1/4) λ (3) Assuming that the sound speed is c. , C = ν · λ, and from equation (1) and equation (3), L = 15c / N · m (4)

For example, c = 340 m / s, N = 3000
If 0 rpm and m = 8 planes, from equation (4), L = (1
5 × 340) / (30000 × 8) = 21.25 (m
m)

Therefore, if the distance L from the rotary polygon mirror 1 to the bottom surface 50a of the optical box 50 is 21.25 mm, the wind noise is caused to interfere with the inside of the optical box 50 and attenuated.
It is possible to avoid noise leaking to the outside, image quality deterioration due to vibration, and the like.

The distance L may be a distance to a rib-shaped opposing wall formed integrally with the optical box 50 or a distance to a rib-shaped opposing wall formed integrally with the lid member 60. . That is, the distance to the opposing wall provided around the rotary polygon mirror 1 may be set to 21.25 mm.

FIG. 2 shows a first modification. This satisfies Expression (4) where a circular recess 50b is provided in the bottom wall of the optical box 50, and the distance from the corner 1a of the rotary polygon mirror 1 as a noise source to the bottom of the recess 50b is L. It is configured as follows.

The radius of the concave portion 50b is larger than the radius of the circumscribed circle of the rotary polygon mirror 1, and the wind noise propagated to the lid member 60 is attenuated by the reflected sound propagating from the bottom surface of the concave portion 50b.

Since it is only necessary to increase the thickness of a part of the optical box, there is an added advantage that the optical box can be downsized.

FIG. 3 shows a second modification. This is the first
In the same manner as the modified example, a curved portion 50c having a radius of curvature L that satisfies Expression (4) is provided on the bottom wall of the optical box 50. The opposing wall surrounding the corner 1a of the rotary polygon mirror 1, which is a noise source, satisfies the condition of Expression (4) in a wide range, and the wind noise due to the reflected propagation sound can be more effectively attenuated. Will be added.

FIG. 4 shows a third modification. This is configured so that the periphery of the rotary polygon mirror 1 is covered with a cover member 9 to prevent contamination of the reflection surface of the rotary polygon mirror 1 and reduce wind noise. Thus, the rotating polygon mirror 1
When the surrounding area is widely covered with a cover member constituting the opposed wall surface, the corner portion 1a where the reflecting surface of the rotary polygon mirror 1 meets the high-speed rotation region having a peripheral speed of 30 m / s or more becomes a corner portion 1a.
At the rear part in the rotation direction of a, a turbulent state occurs as described above, and the Karman vortex S is generated. That is, the conditions under which the Karman vortex S is generated are such that the radius of the circumcircle of the rotating polygon mirror 1 is r, and the gap (distance) between the cover member 9 and the circumcircle of the rotating polygon mirror 1.
Assuming that L is 30 <2π · N · r / 60, 900 <π · r / N (5) From the equation (4), N = 15 c / L · m. <Π · r · c / 60m (6)

It is known that when the gap L between the rotary polygon mirror 1 and the cover member 9 becomes 4 mm or less, the wind pressure in the cover member 9 increases, and a large wind noise is generated.

Therefore, 0.004 <L <π · rc · 60 m (7) For example, c = 340 m / s, m = 8 planes, r = 0.004
If m, from equation (7), 0.004 <L <0.00
The optimum value of the gap is 4 to 9 mm.

FIG. 5 shows the entire scanning optical apparatus, which comprises a light source 51 for generating a light beam such as a laser beam, and a cylindrical light beam for condensing the light beam linearly on the reflection surface of the rotary polygon mirror 1. A lens 51a for deflecting and scanning the light beam by the rotation of the rotary polygon mirror 1;
2 and the photoreceptor 5 on the rotating drum via the mirror 53
4 is imaged. The imaging lens 52 is a spherical lens unit 52
a, a toric lens unit 52b, etc., and a so-called fθ function for correcting the scanning speed and the like of a point image formed on the photoconductor 54.

When the rotary polygon mirror 1 is rotated by the motor, its reflecting surface rotates at a constant speed around the axis of the rotary polygon mirror 1 as shown by an arrow A. As described above, the light source 51
The angle formed by the optical path of the light beam generated by the cylindrical lens 51a and the normal to the reflecting surface of the rotating polygon mirror 1, that is, the angle of incidence of the light beam on the reflecting surface is determined by the rotation of the rotating polygon mirror 1. And the reflection angle also changes with time, so that the point image formed by condensing the light beam on the photoconductor 54 moves in the direction indicated by the arrow Y (main scanning direction).

The imaging lens 52 condenses the light beam (scanning light) reflected by the rotary polygon mirror 1 on the photosensitive member 54 into a point image having a predetermined spot shape, and in the main scanning direction of the point image. Is a complex lens designed to keep the scanning speed of the lens at a constant speed.

The point image formed on the photoreceptor 54 is electrostatically generated by the main scanning by the rotation of the rotary polygon mirror 1 and the sub-scanning by the rotation of the rotating drum having the photoreceptor 54 around its axis. Form a latent image.

Around the photosensitive member 54, a charging device for uniformly charging the surface of the photosensitive member 54, and a charging device for visualizing an electrostatic latent image formed on the surface of the photosensitive member 54 into a toner image. A developing device, a transfer device for transferring the toner image to recording paper or the like (both not shown), and the like are arranged, and recording information by a light beam generated from the light source 51 is printed on recording paper or the like.

The detection mirror 55 reflects the light beam on the upstream side in the main scanning direction with respect to the optical path of the light beam incident on the writing start position Y ₁ of the recording information on the photosensitive member 54.
The light is introduced to the light receiving surface of a light receiving element 56b having a photodiode or the like via a condenser lens 56a. Light receiving element 56b
Outputs a scan start signal for detecting a scan start position (write start position) when the light receiving surface is irradiated with the light beam.

The condenser lens 56a and the light receiving element 56b are arranged between the imaging lens 52 and the rotary polygon mirror 1, and the detection mirror 55 reflects the light beam below the scanning surface of the scanning light.

The light source 51 generates a light beam corresponding to a signal supplied from a processing circuit 57 for processing information from a host computer. The signal given to the light source 51 is
The processing circuit 57 corresponds to information to be written to the photoconductor 54, and the processing circuit 57 uses the signal representing the information corresponding to one scanning line, which is a locus formed by a point image formed on the surface of the photoconductor 54, as one unit, Give to. This information signal is transmitted in synchronization with a scanning start signal given from the light receiving element 56b through the line 56c.

The rotary polygon mirror 1, the imaging lens 52 and the like are housed in an optical box 50, and the light source 51 and the like are mounted on the side wall of the optical box 50. After assembling the rotary polygon mirror 1, the imaging lens 52, and the like to the optical box 50, the lid member 60 is attached to an opening above the optical box 50.

[0045]

Since the present invention is configured as described above, the following effects can be obtained.

The wind noise generated by the high-speed rotation of the rotating polygon mirror leaks out of the optical box and becomes loud,
Further, a scanning optical device with low noise and high image quality can be realized by also acting as a vibration source for vibrating the imaging lens or the like via the lid member or the like, avoiding troubles such as deteriorating the image performance of the image forming apparatus.

By mounting such a scanning optical device, it is possible to greatly contribute to improving the performance of the image forming apparatus.

[Brief description of the drawings]

FIGS. 1A and 1B show a main part of a scanning optical device according to a first embodiment, wherein FIG. 1A is a schematic cross-sectional view thereof, and FIG. 1B explains the reason why wind noise is generated at a corner of a rotary polygon mirror. FIG.

FIG. 2 is a schematic sectional view showing a first modification.

FIG. 3 is a schematic sectional view showing a second modification.

FIG. 4 is a schematic sectional view showing a third modification.

FIG. 5 is a diagram illustrating the entire scanning optical device.

FIG. 6 is a schematic sectional view showing a conventional example.

[Explanation of symbols]

 Reference Signs List 1 rotating polygon mirror 1a corner 3 rotating shaft 5 rotor 6 motor substrate 7 stator 9 cover member 50 optical box 50a bottom surface 50b recess 50c curved portion 60 lid member

 ────────────────────────────────────────────────── ─── Continuing on the front page (72) Inventor Susumu Ikuma 3-30-2 Shimomaruko, Ota-ku, Tokyo F-term in Canon Inc. (reference) 2C362 DA17 DA19 DA20 DA23 2H045 AA33 DA02 DA04 DA41 5C072 AA03 BA13 CA06 DA21 HA02 HA13 XA05

Claims (5)

[Claims] 1. A rotating polygon mirror for deflecting and scanning a light beam, a deflection scanning means including a motor for rotating and driving the rotating polygon mirror, and a housing having the deflection scanning means built therein. A scanning optical device comprising an opposing wall disposed at a distance (L) satisfying the following relationship from an outer peripheral portion of a rotary polygon mirror. L ≒ 15c / N · m where c: speed of sound N: number of rotations of rotating polygonal mirror m: number of reflecting surfaces of rotating polygonal mirror 2. The scanning optical device according to claim 1, wherein the opposed wall surface is a bottom surface of the housing. 3. The scanning optical device according to claim 1, wherein the opposed wall surface is a bottom surface of a recess provided in a bottom wall of the housing. 4. The scanning optical device according to claim 1, wherein the opposed wall surface is provided on a curved portion of a bottom wall of the housing. 5. The scanning optical system according to claim 1, wherein the opposed wall surface is an inner surface of a cover member that covers the rotary polygon mirror, and the distance (L) is configured to satisfy the following relationship. apparatus. 0.004 <L <c · π · r / 60m, where c: sound velocity r: radius of a circumcircle of the rotating polygon mirror m: number of reflecting surfaces of the rotating polygon mirror